Wind-diesel hybrid power generation, Bonaire

Key facts

• Consists of five MAN L27/38 2.87MW diesel engines, 12 Enercon E-44, 900kW wind turbines, a 3MW battery bank and is controlled using a bespoke power management system.
• Developed by Evelop, the wind-diesel power system is owned and operated by ContourGlobal Bonaire and is the sole power generation facility on the island. It integrates renewable (wind) and conventional (diesel) energy production sources to provide reliable power to the island’s 16,500 inhabitants.
• We carried out technical due diligence of the project including a detailed review of the project design, participant capabilities, contracts, technical and financial performance forecasts and permitting.
• We were retained as lenders' engineer throughout construction, to regularly visit the site, report on physical and financial progress and participate in progress meetings. We also provided technical support on site during commissioning.
• The steering committee decided to sell the plant and appointed us to undertake a technical review of the project which focused on the achieved operational performance. We undertook a site inspection, spoke at length with plant operators about the performance of the diesel engines, wind turbines and development of the control system and reviewed operational reports.

Challenges

• A significant technical challenge is the integration of wind turbines and diesel engines into a small autonomous power network to achieve maximum wind penetration, while maintaining system stability.
• The financial success of the project hinged on reaching the desired levels of wind penetration and hence ensuring the success of the control system.
• Since there was no comparable working example of such a system, development of the control strategy was based on the results of power system simulations. The actual dynamic behaviour of the plant would not be fully understood until the system was operational.
• Commissioning of a large wind-diesel project on a small autonomous network presents unique technical challenges. Due to concerns about power supply disruption, it was not possible to evacuate all power to the distribution network and a load bank was used for testing. This meant that the system could not be tested at full load. Also, delivery of the battery bank was delayed which meant that the full functionality of the system could not be tested prior to take over.

Solutions

• In Bonaire, wind-diesel integration was achieved using a combination of the reactive power supply, rapid active power reduction and low voltage ride through functions of the wind turbines, a battery bank, automatic voltage regulator capabilities of the diesel gensets and automatic tap change settings of the main transformers.
• The system is controlled by the power management system which monitors the load demand, frequency, battery charge and wind speed. It then regulates the active and reactive power required from the wind farm according to a series of set points, maintains frequency by despatching or absorbing power using battery and despatches engines so that sufficient positive and negative spinning reserve is always available to meet fluctuations in load and wind speed.
• The control system was of major importance and a focus of our due diligence.
• In effect this was a pilot project and a two-year operation was planned and subsequently undertaken to learn about, develop and tune the control system to achieve optimum performance.

Value and benefits

• We were selected as lenders' engineer because of the multidisciplinary make-up of our company which means that we could bring together a range of specialists with capabilities to cover all aspects of this unique project. A few examples of our key expertise includes wind energy, diesel power, power systems, technology and environmental, regulatory and financial analysis
• Providing comfort to the lenders that the desired performance levels were possible involved a collaborative effort. We confirmed that the specified components were capable of meeting the functional requirements of the system. We carried out a detailed analysis of the static and dynamic power system simulations to confirm that the models accurately replicated the anticipated behaviour of the system and that all perceivable fault scenarios had been considered.